Cervical cancer is one of the most common and deadly cancers among women worldwide. If detected early, cervical cancer and precursor lesions can be treated effectively. A Pap test is the primary screen for cervical cancer and uses morphological analysis to identify suspicious cells. However, a single cytologic examination is relatively insensitive, poorly reproducible and frequently yields equivocal results. Approximately 6% of Papanicolaou (Pap) tests are diagnosed as atypical squamous cells of undetermined significance (ASCUS) and require follow-up testing, and 5-10% of ASCUS patients have undetected cancer. Current guidelines for patients include follow-up Pap testing, testing for human papilloma virus (HPV) and/or colposcopy.
Infection with HPV is associated with cervical cancer and many patients are tested for HPV after an ASCUS Pap test result. The strength of sensitive HPV testing is that it provides extremely high negative predictive value; women who test negative are at low risk for developing cervical cancer. However, the positive predictive value of HPV testing is limited since only a small fraction of HPV positive early lesions progress to high-grade dysplasia and cancer. Thus, HPV detection, even in combination with cytomorphological evaluation, is a test with poor specificity.
In addition, approximately 3% of Pap tests are diagnosed with low-grade squamous intraepithelial lesions (LSIL). Current guidelines for these patients recommend additional monitoring and/or colposcopy. Clinical studies show the majority of these patients are HPV+.
There is significant risk for an ASCUS/HPV+ or LSIL patient to progress to more severe cervical disease and require surgical treatment in the two years following the initial test. The identification of these patients that will progress is impossible based on morphology and HPV infection. Genetic alterations have been identified in the early development of cervical cancer that can predict the patient's risk of disease progression. These aberrations include gross changes in DNA content (e.g. ploidy) and the amplification of both a portion of chromosome 3, specifically locus 3q26, that includes a gene TERC that encodes a subunit the telomerase protein and a portion of chromosome 5, specifically 5p15, that includes a gene, TERT, that encodes another subunit of the telomerase protein, both of which are linked to cell immortality. Studies have demonstrated multicolor fluorescent DNA probes can detect abnormalities in both ploidy, and 3q and 5p copy number by fluorescence in situ hybridization (FISH) with greater sensitivity and specificity than other methods.
The implementation of cervical cancer screening programs has greatly reduced disease incidence and mortality in industrialized countries. However, a single cytological evaluation remains relatively insensitive, hence the need for frequent follow-up investigations. This is attributable to sampling or interpretation errors, and to the fact that some early lesions may not have acquired recognizable phenotypic alterations. Invasive cervical carcinomas develop through increasing stages of cervical dysplasia, to cervical intraepithelial neoplasia (CIN) 1, CIN2, CIN3 and to carcinoma in situ, which is considered a bonafide precancerous lesion that requires surgical intervention. However, only about 15% of all low-grade dysplastic lesions follow this path of linear progression. Pap and HPV tests are indirect methods for determining the presence of cervical dysplasia or cancer. Therefore, there is a continuing unmet need for the methods of using molecular markers for directly identifying the presence of dysplasia or cancer and monitoring disease progression.